Tertiary recovery operation

ABSTRACT

At the conclusion of a secondary recovery operation in a direct line drive, after breakthrough of the driving fluid at the production wells in alternate series of a pair of production wells and an intermediate injection well having a different rate of injection of driving fluid, production is continued via the wells in the remainder of alternate series until breakthrough, and thereupon, for tertiary recovery, by the imposition of a new set of flow gradients, the original injection wells are shut in, the production wells with the initial breakthrough are converted into injection wells and production is continued via the remainder of the production wells.

United States Patent [191 Altamira et al.

[451 Apr. 15, 1975 TERTIARY RECOVERY OPERATION [75] Inventors: AnthonyF. Altamira, Dhahran,

Saudi Arabia; Donald L. Hoyt,

Houston, Tex.

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Apr. 8, 1974 21 Appl. No.: 458,918

Primary Examiner-Stephen .1. Novosad Attorney, Agent, or FirmThomas H.Whaley; Carl G. Ries [57] ABSTRACT At the conclusion of a secondaryrecovery operation in a direct line drive, after breakthrough of thedriving fluid at the production wells in alternate series of a pair ofproduction wells and an intermediate injection well having a differentrate of injection of driving fluid, production is continued via thewells in the remainder of alternate series until breakthrough, and

thereupon, for tertiary recovery, by the imposition of a new set of flowgradients, the original injection wells are shut in, the productionwells with the initial breakthrough are converted into injection wellsand production is continued via the remainder of the production wells.

5 Claims, 6 Drawing Figures PATENTEDAPR 1 SW5 3. 877, 521

SHEET 1 15 g TERTIARY RECOVERY OPERATION FIELD OF THE INVENTION Thisinvention relates generally to the production of hydrocarbons fromsubterranean hydrocarbon-bearing formations, and more particularly, to amethod for increasing the efficiency of the production of hydrocarbonstherefrom.

DESCRIPTION OF THE INVENTION In the production of hydrocarbons frompermeable subterranean hydrocarbon-bearing formations, it is customaryto drill one or more boreholes or wells into the hydrocarbon-bearingformation and produce formation fluids including hydrocarbons, such asoil, through designated production wells, either by the naturalformation pressure or by pumping the wells. Sooner or later, the flow ofhydrocarbon-bearing fluids diminishes and/or ceases, even thoughsubstantial quantities of hydrocarbons are still present in thesubterranean formations.

Thus, secondary recovery programs are now an essential part of theoverall planning for exploitation of oil and gas-condensate reservoirsin subterranean hydrocarbon-bearing formations. In general, thisinvolves injecting an extraneous fluid, such as water or gas or otherdisplacing compounds, into the reservoir zone to drive formation fluidsincluding hydrocarbons toward production wells by the process commonlyreferred to as floodingf Usually, this flooding is accomplished byinjecting through wells drilled in a pattern, e.g., the direct andalternating line drive and the more commonly used 5-spot pattern.

When the driving fluid, e.g., water from the injection well reaches theproduction wells of a direct line drive, the areal sweep efficiency is57%. By continuing production considerably past breakthrough it ispossible to produce more of the remaining unswept portion of theformation, although continued injection will not reduce oil saturationmuch further.

In secondary recovery programs, sweepout is generally given as thepercent of available volume invaded by the driving fluid at breakthroughinto the production wells. This is done because production pastbreakthrough, while nearly always attempted, is an uncertain thing. Forexample, assuming water to be the driving fluid, the water-oil ratio mayrise gradually over a period ofmany years or a well or pattern may go to100% water within months. Much depends on how easily and quickly thewater phase envelops the well to such an extent that the relativepermeability to oil is reduced to zero.

One of the reasons for the rapid rise in water production is that thedriving fluid, e.g., water, in reaching the production well, has openedchannels through which the water flows preferentially, therebyby-passing much inplace hydrocarbons, such as oil. Continued flowwidens'the channels, stripping some of the adjoining hydrocarbons oreven opens up a few more channels, but it is observed generally that alarge quantity of additional driving fluid, e.g., water, is required toproduce ever decreasing amounts of hydrocarbons.

A procedure to provide for better recovery more quickly than in thepresent procedures involves the changing of direction of the flowgradients shortly after breakthrough. A simple and effective procedureafter initial breakthrough is to switch the injection of driving fluidto a converted production well offset from the line between an injectionwell and an adjacent production well. The original injection well havingbeen shut in, the new flow paths established from the convertedproduction well, crossing established water channels, break them up andmove trapped or bypassed hydrocarbons toward the other production well.

In addition, the driving fluid injected from the converted productionwell will be sweeping through a region between original production wellswhich is nearly always of higher hydrocarbon saturation than the regionexisting between the original injection and production wells.

From a potentiometric model study, by continued production pastbreakthrough of a secondary recovery program in a direct line drive,using the same injection and production wells, the sweepout caneventually approach 95% if the well continues to produce. However, in anactual hydrocarbon reservoir, the cusp of the driving fluid swells sorapidly in this case that the wateroil ratio rises very quickly to over90%. By this time the water saturation around the well will be so highthat continued flow of the oil phase is very unlikely and the patternmay have to be abandoned at about total sweepout.

With the intermediate injection wells of the series of the line drivepattern of wells being closed in and the alternate production wells ofthe adjacent series of wells being converted to injection wells, theinterface positions at breakthrough of driving fluid from the convertedwells shows that the cusp of previously injected fluid is still small,and the water-oi] production ratio by calculations based on shape isabout 25%, and the pattern sweepout is now 92%. This principle ofimposing new flow gradients by changing the functions of certain wellscan be applied in virtually any reservoir whether drilled on a patternor not.

SUMMARY OF THE INVENTION It is an overall object of the presentinvention to provide an improved recovery procedure involving threewells in line as one of a series in a direct line drive as part of awell pattern arrangement for exploiting a hydrocarbon-bearing formationwith alternate series of wells having different rates of injection, byshutting in the intermediate injection wells following breakthrough ofthe driving fluid at all of the production wells, thereafter convertingthe production wells in alternate series of the pattern sufferingbreakthrough into injection wells while maintaining production from theremainder of the wells of the series.

A three-well group of a series in a direct line drive is arranged inline so that the intermediate well is completed for injection and theremaining two wells are completed for production. Flooding is initiatedat the intermediate well by injection of a driving fluid, such as water,thereinto at different rates in alternate series, and proceeds untilbreakthrough of the flood front occurs at all of the production wells,at which time injection via the intermediate wells is terminated and thewells shut in. Then, the original production wells in the alternateseries with initial breakthrough are converted to tertiary injectionwells while the remainder of the production wells, viz., those in theother alternate series, are maintained on their original function.

Other objects, advantages and features of this invention will becomeapparent from a consideration of the specification with reference to thefigures of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 discloses the symbols used inthe remaining figures of the drawing;

FIG. 2 illustrates the principle of the invention;

FIGS. 3 and 4 illustrate the first and second phases of a secondaryrecovery program of a direct line drive;

FIG. 5 discloses the termination of the tertiary phase of a direct linedrive recovery procedure according to this invention; and

FIG. 6 discloses the differences in water cuts during production pastbreakthrough of a direct line drive and a cross flood line drive.

The objects of the invention are achieved by shutting in all of theintermediate injection wells at time of the breakthrough of the drivingfluid at all of the production wells in the alternate series having thelower rate of injection thereof and converting the production wells inthese alternate series with the initial breakthrough of the drivingfluid into injection wells to produce a new set of flow gradient forcesto inhibit cusp expansion at the remainder of the production wells inthe other alternate series.

The specification and the figures of the drawings schematically discloseand illustrate the practice and the advantages of the invention,examples of which have been observed in potentiometric model studies.which simulate secondary and tertiary recovery operations. The modelstudies indicate a sweepout obtained in an ideal reservoir, although therecovery from an actual sweepout of a particular field may be greater orless. depending on field parameters.

Throughout the figures of the drawings. the same symbols will bemaintained as disclosed in FIG. 1, viz., a solid circle indicates aproduction well, a crossed open circle a shut-in well, an open circlewith a first quadrant arrow indicates a low quantity secondary injectionwell, a double open circle with a first quadrant arrow indicates a highquantity secondary injection well, and an open circle with a fourthquadrant arrow, a converted tertiary injection well.

FIG. 2 illustrates the manner of changing the direction of the flowgradients shortly after breakthrough of the driving fluid at aproduction well. Thereupon, the original injection well is shut in,since channels for the flow of the driving fluid have been established,and the direction of the flow gradients is changed by switching theinjection of the driving fluid to a converted production well, offsetfrom the line between the original injection well and the productionwell with breakthrough. The indicia in this figure are self-explanatoryof the phenomenon desired.

Referring to FIG. 3, there is disclosed symbolically the first phase ofa direct line drive in a secondary recovery procedure, wherein in eachseries, the intermediate injection wells are aligned with the productionwells with a d/a of l, and the production and/or injection rates aresuch that those production wells in a line substantially perpendicularto the line between the intermediate injection wells and the productionwells in each series, will experience breakthrough in alternate serieswith a sweep efficiency of 57% in each pattern unit (of area 2 da).

Referring to FIG. 4 and following breakthrough as indicated by the cuspformations in FIG. 3, all the production wells in the series of thedirect line drive program are maintained on production, and as indicatedin this figure, the injection of the driving fluid is at an equal rateuntil breakthrough occurs at the production wells in the other alternateseries of the program.

Thereafter, as indicated in FIG. 5, all of the intermediate injectionwells are shut in, the production wells in the alternate series whichhad undergone the original breakthrough of the driving fluid areconverted to injection wells, and the remaining production wells in theother alternate series remain on production, as either secondary ortertiary driving fluid is injected into the formation via the convertedproduction wells, until the calculated sweepout of the overall patternhas reached about 92%, as disclosed in FIG. 6. This figure disclosesthat with the cross flood, the water cut decreases with an increase insweep efficiency to more than 92%.

Thus, there has been shown and described the manner by which a tertiaryrecovery operation may be initiated with favorable economic resultsfollowing the conclusion of a secondary recovery operation followingbreakthrough of driving fluid at the production wells, by introducing anew set of flow gradients to affect cusp formation and to displacehydrocarbons otherwise trapped in flow channels established by priorflow graclients.

As will be apparently to those skilled in the art in the light of theaccompanying disclosure. other changes and alterations are possible inthe practice of this invention without departing from the spirit orscope thereof.

We claim:

1. During a recovery operation, a method of producing formation fluidsincluding hydrocarbons from a subterranean hydrocarbon-bearing formationby a direct line drive which comprises penetrating said formation with aplurality of wells disposed in a linear pattern and comprising a seriesof a pair of production wells and an intermediate injection well,injecting an extraneous driving fluid into said formation via theintermediate injection well to displace formation fluids includinghydrocarbons in said formation toward said production wells, producingsaid formation fluids including hydrocarbons from said formation viasaid production wells, said producing of said formation fluids and saidinjecting of said extraneous fluid being at such rates that theproduction wells in alternate series of wells of said pattern undergobreakthrough of said extraneous fluid initially, thereafter continuingproducing said formation fluids while injecting said extraneous fluiduntil breakthrough of said driving fluid at the production wells in theseries of wells alternate to those which had undergone breakthroughinitially, thereupon initiating an additional recovery operation byimposing a new set of flow gradients comprising the steps of shutting inthe intermediate injection wells in said series and convertingproduction wells in said series which had undergone breakthrough of saiddriving fluid initially into injection wells, and thereafter producingformation fluids via the remainder of said production wells.

2. In the method as defined in claim 1, said intermediate injection welland said pair of production wells being disposed in a common row of aseries thereof.

3. In the method as defined in claim 2, said intermediate injection welland said production wells being disposed respectively in common rows.

LII

6 troducing said driving fluid via said intermediate injection wellsbeing equal and the rate of producing formation fluids via saidproduction wells being maintained at a constant rate following theinitial breakthrough of said driving fluid at said alternate series ofwells.

1. DURING A RECOVERY OPERATION, A METHOD OF PRODUCING FORMATION FLUIDSINCLUDING HYDROCARBONS FROM A SUBTERRANEAN HYDROCARBON-BEARING FORMATIONBY A DIRECT LINE DRIVE WHICH COMPRISES PENETRATING SAID FORMATION WITH APURALITY OF WELL DISPOSED IN A LINEAR PATTERN AND COMPRISING ASERIES HOFA PAIR OF PRODUCTION WELLS AN INTERMEDIATE INJECTION WELL, INJECTING ANEXTRANEOUS DRIVING FLUID INTO SAID FORMATION VIA THE INTERMEDIATEINJECTION WELL TO DISPLACE FORMATION FLUIDS INCLUDING HYDROCARBONS INSAID FORMATION TOWARD SAID PRODUCTION WELLS PRODUCING SAID FORMATIONFLUIDS INCLUDING HYDROCARBONS FROM SAID FORMATION VIA SAID PRODUCTIONWELLS, SAID PRODUCING OF SAID FORMATION FLUIDS AND SAID INJECTING OFSAID EXTRANEOUS FLUID BEING AT SUCH RATES THAT THE PRODUCTIOM WELLS, INALTERNATE SERIES OF WELLS OF SAID PATTERN UNDERGO BREAKTHROUGH OF SAIDEXTRANEOUS FLUUID INITIALLY, THEREAFTER CONTINUING PRODUCING SAIDFORMATION FLUIDS WHILE INJECTING SAID EXTRANEOUS FLUID UNTILBREAKTHROUGH OF SSAID DRIVING FLUID AT THE PRODUCTION WELLS IN THESERIES OF WELLS ALTERNATE TO THOSE WHICH HAD UNDERGONE BREAKTHROUGHINITIALLY, THEREUPON INITIATING AN ADDITIONAL RECOVERY OPERATION BYIMPOSING A NEW SET OF FLOW GRADIENTS COMPRISING THE STEPS OF SHUTTING INTHE INTERMEDIATE INJECTION WELLS IN SAID SERIES AND COVERTING PRODUCTIONWELLS IN SAID SERIES WHICH HAD UNDERGONE BREAKTHROUGH OF SAID DRIVINGFLUID INITIALLY INTO INJECTION WELLS, AND THEREAFTER PRODUCING FORMATIONFLUID VIA THE REMAINDER OF SAID PRODUCTION WELLS.
 2. In the method asdefined in claim 1, said intermediate injection well and said pair ofproduction wells being disposed in a common row of a series thereof. 3.In the method as defined in claim 2, said intermediate injection welland said production wells being disposed respectively in common rows. 4.In the method as defined in claim 1, the rates of producing formationfluids and injecting extraneous driving fluid being held constant as atthe time of breakthrough of said driving fluid initially at theproduction wells of alternate series of said linear pattern.
 5. In themethod as defined in claim 1, the rate of introducing said driving fluidvia said intermediate injection wells being equal and the rate ofproducing formation fluids via said production wells being maintained ata constant rate following the initial breakthrough of said driving fluidat said alternate series of wells.